The invention lies in the telecommunications field. More specifically, the invention relates to a method and a device for data transmission via an air interface between radio stations in a radio communications system.
Radio communications systems, also referred to as wireless systems, serve to transmit data with the aid of electro-magnetic waves via an air interface between a transmitting and a receiving radio station. An example of a radio communications system is the well-known GSM mobile radio network, in which a channel formed by a narrowband frequency band and a time slot is provided in each case for transmitting a subscriber signal. Due to the fact that a subscriber signal is separated on a channel in frequency and time from remaining subscriber signals, the receiving radio station can detect the data of this subscriber signal.
It has become known from the GSM mobile radio system to make use of training sequences embedded in the data of the subscriber signal which are known at the receiving end and serve to determine channel coefficients. The channel coefficients thereby simulate the radio transmission channel and facilitate the compensation of interference during subsequent data detection.
The frequency band available to the GSM mobile radio network is limited and leads increasingly to capacity bottlenecks, in particular in areas of high subscriber density. The capacity of the GSM mobile radio network is thereby limited by the number of the channels possible in a radio cell. A possibility of increasing this capacity is to introduce a so-called half rate transmission. The half rate transmission presupposes for voice an improved source coding so that only half of the previously required time slots suffice to transmit the same quantity of data.
Half-rate coding, however, can be applied only to voice information.
It is accordingly an object of the invention to provide a method and a receiving device in a data transmission system, which overcomes the above-mentioned disadvantages of the heretofore-known devices and methods of this general type and which achieves an increase in capacity independently of the significance of the data to be transmitted.
With the foregoing and other objects in view there is provided, in accordance with the invention, a method of transmitting data via an air interface between radio stations in a radio communications system, which comprises the following steps:
grouping data to be transmitted into message blocks at a transmitting end, the message blocks respectively containing additional symbols of a training sequence;
simultaneously transmitting at least two message blocks with mutually different training sequences on a channel designated by a frequency band and a time slot;
carrying out at least two channel estimates per channel at a receiving end with knowledge of the different training sequences; and
respectively detecting the data of the at least two simultaneously transmitted message blocks for each channel based on the separate channel estimates.
In other words, the data to be transmitted are grouped into message blocks at the transmitting end and the message blocks are provided with respective additional symbols of a training sequence. Thereupon, at least two message blocks with different training sequences are simultaneously transmitted on a channel, whereupon the data are detected at the receiving end with knowledge of the at least two training sequences. While the summary and the detailed description generally refer to at least two message blocks, the method can also be applied for a larger number of message blocks.
By virtue of the fact that it is ensured when selecting the training sequences that the latter always differ from one another in conjunction with simultaneously transmitted message blocks, the subscriber signals can be separated at the receiving end by means of this characteristic of a message block. The data to be transmitted in the two message blocks can be arbitrary in this case. There is no need to heed any restrictions for these data and the ratio of the individual symbols to one another. Thus, when data of the two message blocks are evaluated the method according to the invention achieves an increase in capacity at least by a factor of 2 which is not limited only to voice information, but can also be applied to further services.
In accordance with an added feature of the invention, the data of the at least two message blocks are detected at the receiving end.
In accordance with an alternative feature of the invention, the data of one message block are detected at the receiving end, and the knowledge of the further message block is used to improve the detection. An improvement in the interference immunity of the connection is thereby achieved. The interference from neighboring cells can thus also be compensated. Consequently, it is possible to permit relatively severe interference in the system, as a result of which either an improved reuse of frequency or a higher subscriber density becomes possible.
In accordance with another feature of the invention, radio stations simultaneously transmitting on one channel are synchronized, and according to a further feature the received data which are simultaneously transmitted in the same channel are synchronized. Different propagation paths of the transcriber signals lead to different instants of arrival at the receiving radio station, so that it is particularly important to use synchronization to tune the arrival of the two message blocks to one another, and thus to facilitate the following steps for channel estimation and data detection. The synchronization is prepared by signaling to the transmitting radio stations, which can thereupon set the transmission instant. The synchronization can also be performed at the receiving end; in this case, there is no need to signal to the transmitting radio stations.
In accordance with a further feature of the invention, the synchronizing step comprises setting a temporal deviation in an arrival of the at least two message blocks at the radio station at the receiving end which is smaller than a symbol length. In other words, a temporal deviation in the arrival of the at least two message blocks at the radio station at the receiving end which is smaller than a symbol length is advantageously set by the synchronization. Thus, if the transmission instants of the transmitting radio station are set in each case of signaling in such a way that there are a slight deviation between the instants of the occurrence of the at least two message blocks, it is possible to keep a bit error rate of the data transmission low by improved detection.
In accordance with again an added feature of the invention, at least two training sequences are allocated to a transmitting radio station. A doubled data rate is rendered possible for this radio station by this measure. There is no need for additional outlay on hardware for this radio station, all that is required is to adapt the signal processing as appropriate in the receiving radio station. This can be performed, as the case may be, by reprogramming the appropriate signal processor.
If the radio stations are designed as mobile stations or base stations of a digital mobile radio network, the direction of transmission from the mobile station to the base station is designated as uplink direction, and the direction of transmission from the base station to the mobile station is designated as downlink direction. In accordance with a development of the invention, different transmission rates are used in the uplink direction and downlink direction.
Consequently, asymmetrical services are possible which do better justice to the particular features of the requirements placed on the data to be transmitted. It is advantageous for message blocks of higher data rates to be used in the uplink direction than the downlink direction. That is to say, the mobile stations receive as previously, but they transmit simultaneously with other mobile stations on one channel, and thereby increase the data rate in the uplink direction. Consequently, there is no need to change the circuit engineering of mobile stations; it is possible to achieve a doubling of the capacity of a data transmission in the uplink direction in the base station by appropriate adaptation of the signal processing.
The method according to the invention exhibits particular advantages when the transmitted data are transmitted in accordance with a packet data service (GPRS General Packet Radio Services). In the case of this service, the data rates must be easily changeable, and flexible utilization of the radio resources of the air interface must be possible. This can be implemented by means of the method according to the invention.
In accordance with again a further feature of the invention, the detecting step comprises evaluating the at least two training sequences to obtain a message block-related channel estimation.
With the above and other objects in view there is provided, in accordance with the invention, a receiving device for data transmitted via an air interface between radio stations in a radio communications system, comprising:
a channel estimator for simultaneous channel estimation of at least two message blocks simultaneously transmitted in one channel of an air interface designated by a frequency band and a time slot, the channel estimator evaluating for each channel at least two connection-specific training sequences transmitted within the message blocks in addition to the data, and determining channel coefficients in each case; and
a detector connected to the channel estimator for respectively detecting data for the at least two message blocks with knowledge of the at least two separately determined channel coefficients.
In accordance with yet an additional feature of the invention, the channel estimator is programmed to simultaneously determine at least two sets of channel coefficients by minimizing, for received training sequences, a deviation of received data relative to reference data generated in at least two channel models with channel coefficients.
In accordance with yet another feature of the invention, the detector is programmed to consider at least four transitions from previous detection states xcex93i to a new detection state xcex93xe2x80x2 for applying Viterbi algorithm, and to determine the new detection state in accordance with the equation xcex93xe2x80x2=min(xcex93i+xcex94i)|i=0 . . . 3, whereby xcex94i is a Euclidean spacing between a received symbol and a reference symbol.
In accordance with a concomitant feature of the invention, at least one decoder is provided which takes account of soft outputs sxe2x80x21, sxe2x80x22 calculated according to
sxe2x80x21=(xcex93iminand2+xcex94iminand2)xe2x88x92(xcex93imin|1+xcex94imin|1) and sxe2x80x22=(xcex93iminand1+xcex94iminand1)xe2x88x92(xcex93imin|2+xcex94imin|2).
As noted above, the device is advantageously utilized in a mobile station or a base station of a digital mobile radio network.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in method and receiver for data transmission, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.